1. Field of Invention
The present invention relates to a source driver, and more particular, to a source driver that includes a feedback mechanism to adjust a slew rate of an output buffer included in the source driver.
2. Description of Related Art
In recent years, liquid crystal displays (LCDs) have become dominant in the market due to the advantages of low power consumption, zero radiation, and high space utilization. The source driver is an important component in the driving system of the display device, which is used for converting a digital video signal to a driving voltage and providing the driving voltage to a pixel electrode in association with a certain enabled scan line. The driving voltages provided to the pixel electrode are not as good as expected because of the panel loading effect and the process variation so that the source driver utilizes the output buffers to enhance the driving abilities of its driving channels.
Generally, an operational amplifier is utilized to implement the output buffer in the source driver. The operational amplifier has many specification parameters, such as a unity-gain frequency, phase margin, power consumption, common-mode rejection ratio, power-supply rejection ratio, input common mode range, slew rate, and noise. The slew rate refers to a change rate of an output voltage, which is generally defined as volt/second (or microsecond). It should be noted that, the slew rate may affect an image quality of the LCD directly. The higher the slew rate is, the shorter the time required for the source driver to provide correct analog signals to a display panel will be. On the contrary, the lower the slew rate is, the longer the time required for the source driver to provide correct analog signals to the display panel will be. As a result, the lower slew rate may lead to blurring or flickering of images.
Moreover, the display panels with the same size fabricated by different factories may have different loads. Under the same system specification, e.g. scanning frequency, resolution of the display panel, or size of the display panel, the output buffer with limited driving ability or unadjustable slew rate may conform to the display panels fabricated by a minority of factories, so the application scope of the output buffer is limited.